word problem

Question

serial numbers for a product are to be made using 4 letters followed by 4 numbers. if the letters are to be taken from the first 9 letters of the alphabet with no repeats and the numbers are taken from 0-9 with repeats possible, how many serial numbers can be generate

Answer 1

9P4 * 10^4 = 9*8*7*6*10^4

Answer 2

From the letters you have 9*8*7*6 choices. From the numbers you have 10*10*10*10. Multiply all together and you will have your answer.